The present invention generally relates to semiconductor processing and, more particularly, to in-situ thickness measuring of thin films during semiconductor processing.
In the semiconductor industry, there is a continuing trend toward higher device densities. To achieve these high densities there has been and continues to be efforts toward scaling down device dimensions (e.g., at submicron levels) on semiconductor wafers. In order to accomplish such high device packing density, smaller and smaller feature sizes are required. This may include the width and spacing of interconnecting lines, spacing and diameter of contact holes, and the surface geometry such as corners and edges of various features.
The requirement of small features with close spacing between adjacent features requires high resolution photolithographic processes. In general, lithography refers to processes for pattern transfer between various media. It is a technique used for integrated circuit fabrication in which a silicon slice, the wafer, is coated uniformly with a radiation-sensitive film, the resist, and an exposing source (such as optical light, x-rays, or an electron beam) illuminates selected areas of the surface through an intervening master template, the mask, for a particular pattern. The lithographic coating is generally a radiation-sensitive coating suitable for receiving a projected image of the subject pattern. Once the image is projected, it is indelibly formed in the coating. The projected image may be either a negative or a positive image of the subject pattern. Exposure of the coating through a photomask causes the image area to become either more or less soluble (depending on the coating) in a particular solvent developer. The more soluble areas are removed in the developing process to leave the pattern image in the coating as less soluble polymer.
A large variety of xe2x80x9cthin filmsxe2x80x9d are used in the fabrication of semiconductor devices. These films may be thermally grown or deposited from a vapor phase. The thin films may, for example, be metals, semiconductors (e.g., oxides, nitrides, and poly, oxynitrides), or insulators. Due to the extremely fine patterns and dimensions of features that are formed on a substrate, thickness of a deposited film is a significant factor in achieving desired critical dimensions. By way of example, very low densities of both particulate defects and film imperfections, such as pinholes, become critical for the small linewidths, high densities, and large areas necessary for VLSI. These small geometries also create highly rugged topography for overlying films to cover.
The formation of thin films is accomplished by a variety of techniques, which can conceptually be divided into two groups: 1) film growth by interaction of vapor-deposited species with the substrate; and 2) film formation by deposition without causing changes to the substrate material. The first category includes thermal oxidation and nitridation of single crystal silicon and polysilicon, and the formation of silicides by direct reaction of a deposited metal and the substrate.
The second group includes other subclasses of deposition: a) chemical vapor deposition, or CVD, in which solid films are formed on a substrate by the chemical reaction of vapor phase chemicals that contain the required constituents; b) physical vapor deposition, or PVD, in which the species of the thin film are physically dislodged from a source (to form a vapor). The species is transported across a reduced pressure region to the substrate to form the solid thin film.
Typically several process steps, which may include thin film growth and/or deposition, are required to form a desired feature. Typically, measurements concerning the thickness of films applied during such deposition processes are made after corresponding processing steps have been completed. Slight variations in the film thickness, however may greatly affect the operation of a resulting semiconductor device.
Consequently, if the thickness is not within an expected range, the process parameters may need to be modified and the process steps repeated to produce a thin film having the desired film thickness. In addition, because the thickness is measured after the process has been completed, it tends to be difficult to determine which parameters should be modified and the extent to which they should be modified to achieve a desired film thickness.
The present invention relates to a system and method for providing in-situ thickness and process monitoring to help achieve a desired feature thickness. By monitoring film thickness during semiconductor processing, one or more process control parameters may be adjusted to help achieve a desired film thickness. As a result, the number of process steps required to achieve the desired film thickness may be reduced, providing a more efficient and economical process.
One aspect of the present invention provides a semiconductor processing system. The system includes a processing chamber operable to form a thin film on a substrate located in the chamber. A measurement system performs in-situ thickness measurements of the thin film being formed and provides a measurement signal indicative of the measured thickness. In accordance with another aspect of the present invention, the measured thickness further may be employed for process control to help achieve a desired film thickness.
Yet another aspect of the present invention provides a method to facilitate formation of a thin film on a substrate. The method includes forming the thin film on the substrate and measuring film thickness of the thin film while being formed at the substrate.
To the accomplishment of the foregoing and related ends, certain illustrative aspects of the invention are described herein in connection with the following description and the annexed drawings. These aspects are indicative, however, of but a few of the various ways in which the principles of the invention may be employed and the present invention is intended to include all such aspects and their equivalents. Other advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the drawings.